Characterisations of New Nd³⁺-Doped Scheelite-Type Molybdates for Laser Materials

Abstract

The necessity to develop new laser materials was our motivation to study a new family of molybdates activated by the Nd³⁺ ions, which crystallizes in the scheelite-type structure (the tetragonal symmetry, the space group I4_1∕a ). A series of Cd_{1 − 3} xNd_{2x_x}MoO₄ solid solutions with concentration of Nd³⁺ ions from 0.1 to 66 mol % with respect Cd²⁺ ions have been successfully synthesized by a high-temperature annealing, using CdMoO₄ and Nd₂(MoO₄)₃ as the starting materials. Structural and spectroscopic characterizations of Nd³⁺in substitution of Cd²⁺ were carried out. The Nd³⁺ ions in this matrix most probably occupy two non-equivalent symmetry sites (see Fig. 45.1). The substitution of Cd²⁺ by trivalent Nd³⁺ cations leads to the formation of cationic vacancies in a framework (which are denoted in the chemical formula as _ ) and its concentration depends essentially on the composition of initial CdMoO₄/Nd₂(MoO₄)₃ mixtures. The analysis of the morphology using SEM reveals high homogeneity of the spherical-shape products with the average grain size of about 10 μm. The optical analysis and the laser performance parameters suggest Cd_{1 − 3x}Nd_{2x_x} MoO₄ as a potential laser powder material: both the values of the absorption cross-section and the very strong emission of the⁴F_3∕2− > ⁴I_11∕2 laser channel of Nd³⁺ recorded under Xe lamp excitation or OPO laser pumping, as well as, the radiative lifetimes of IR luminescence are appropriate for potential applications of this phosphor as a solid-state laser. Our earlier studies have shown that the presence of the cationic vacancies in the framework may significantly improve the laser parameters (Guzik et al., J Mater Chem 22:14896, 2012).